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991.
A single laboratory validation (SLV) study was conducted for a liquid chromatography (LC) method for the determination of total and all-trans-beta-carotene in a variety of dietary supplements, including multivitamin tablets, softgels, capsules, and beadlet raw materials. Extraction variants were developed for the different types of supplements tested based upon the supplement type and level of beta-carotene. Water dispersible formulations such as powders, emulsions, tablets, and capsules were enzymatically digested with protease and extracted with dichloromethane-ethanol. Oily suspensions were directly dissolved in dichloromethane-ethanol. After appropriate dilution or concentration, the extracts were chromatographed by using either a reversed-phase C18 column or, in products containing high amounts of alpha-carotene, a reversed-phase C30 column. The LC systems provided linear responses in the range of 0.1-50 microg beta-carotene/mL. The main geometrical isomers of beta-carotene (all-trans, 9-cis, 13-cis, and 15-cis) were well separated from each other and from other carotenoids such as a-carotene, cryptoxanthin, lutein, lycopene, and zeaxanthin. Duplicate determinations of total beta-carotene performed by 2 technicians in 8 different test materials on 5 different days resulted in relative standard deviations of 1.2-4.4%. Recoveries determined for supplements and beadlet raw material spiked with beta-carotene levels of 10 microg to 100 mg/test portion and 0.2-40%, respectively, ranged from 97.5 to 102.1%. On the basis of the accuracy, precision, and recovery results from the SLV study, the method is suggested for a collaborative study on the determination of total and all-trans-beta-carotene in dietary supplements. 相似文献
992.
Dey A Glaser T Moura JJ Holm RH Hedman B Hodgson KO Solomon EI 《Journal of the American Chemical Society》2004,126(51):16868-16878
Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the mu(2)S(sulfide), mu(3)S(sulfide), and S(thiolate) ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe(3+) and Fe(2.5+) components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38% vs 61%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm(-1) vs -360 cm(-1), respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter lambda2/k(-), leads to an S = 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe(3+) center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite. 相似文献
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994.
Guć Maria Reszke Edward Cegłowski Michał Schroeder Grzegorz 《Plasma Chemistry and Plasma Processing》2019,39(4):1001-1017
Plasma Chemistry and Plasma Processing - A new direct-current microwave argon plasma source was designed and constructed for use in mass spectrometry. Solid samples and analytes on solid materials... 相似文献
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996.
Edward J Behrman 《Chemistry Central journal》2009,3(1):1-3
An improved synthesis of 3-hydroxy-4-pyridone via an Elbs oxidation of 4-pyridone and isolation of 4-pyridone-3-sulfate is described. 相似文献
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999.
HOU Xiao-Min CHEN Ming-Huang PENG Qi CHEN Li-Qing Meehan Edward J HUANG Ming-Dong 《结构化学》2007,26(11):1303-1307
β-Trichosanthin,a type 1 ribosome-inactivating protein (RIP) isolated from the root tuber of Trichosanthe kirilowii Maxim,is an isoform of trichosanthin. Here we report its crystal-lization in two crystal forms using the hanging-drop vapor-diffusion method. The form A and form B crystals belong to the orthorhombic space group P212121 and monoclinic space group P21,respectively. X-ray data have been collected to 1.6 and 1.2 resolution for form A and form B crystals,respectively,using a synchrotron source. 相似文献